If you consider storage in isolation, Backblaze does seem to be the best deal. However, there may be bundles that include storage that are a better deal if you need the other things in the bundle.
For example if you have sufficient need for Microsoft Office programs to justify a Microsoft 365 subscription, that comes with 1 TB of OneDrive on the Personal subscription ($6.99/month, $69.99/year).
Most backup programs seem to know how to work with OneDrive directly or know how to use rclone which knows how to work with OneDrive [1].
If you need more than 1 TB, OneDrive becomes less attractive. It seems you can add another 1 TB for $9.99/month, but unless you have to all your storage be in one place, it would be cheaper to get your second TB at Backblaze. (And if you need 2 TB in one one place, buying 2 TB at Backblaze + An MS 365 Personal subscription would be the same price as an MS 365 Personal + 1 TB Extra OneDrive, and the former gives you your 2 TB in one place at BB and 1 TB at OneDrive).
The Family subscription ($9.99/month or $99.99/year) includes 6 TB of OneDrive, but it is partitioned into 6 separate 1 TB shares for 6 people on the account. A person is identified by an email address, so there is nothing stopping you from making 5 fake people, and one person can give another write access to folders on their OneDrive, so you could cobble together a scheme to use all 6 TB but there would be some hassle.
I tried doing that once, having the fake person give the real me write access to a folder. I then uploaded a bunch of files to that shared folder from my regular account. Shortly afterward the fake person got disabled for TOS violations (but could be reenabled via a simple automated process). I'm not sure what the issue was, but what I uploaded was a bunch of Springer ebooks to from the large collection that Springer made freely downloadable early during COVID so that I could read them on my iPad. It could be that triggered some sort of anti-piracy measures.
If you can find a way to make it work, though, 6 TB for $9.99/month or $99.year is a good deal even if you don't need the Office apps.
[1] https://rclone.org/onedrive/